A torque wrench is used to exert a given torque on connecting elements, such as screws or nuts. For this purpose, torque wrenches comprise a wrench lever with a grip and a wrench head, referred to as head portion hereafter. Often, a coupling in the form of a square pilot is provided at the wrench head to receive an insert tool. Different insert tools for rotating screws or nuts can be fixed on the square pilot. A force exerted on the grip by a user in the operating direction is transferred from the wrench lever to the wrench head and generates a torque on a screw or nut through the insert tool. In order to measure the exerted torque the torque wrench is provided with a measuring device. With further devices the measured torque is continuously displayed or the reaching of a given torque is indicated.
The measuring device of the torque wrench is subjected to common wear and tear symptoms. The torque wrench must be calibrated from time to time with an operating device to check if a torque measured with the measuring device is the same as an exerted torque. For this purpose a carrier with a transducer and a grip holder is provided in the operating device. The head portion of the torque wrench is tightly coupled to the transducer, for example with the square pilot. The grip of the torque wrench is fixed by the grip holder.
Then a torque is exerted to the head portion of the torque wrench by a deflecting mechanism. This torque is measured by the transducer und displayed in a display provided at the operating device, for example at the transducer. The torque displayed by the torque wrench or a torque set for the torque wrench for a release can be tested by comparison with the torque displayed on the display.
With known operating devices for testing torque wrenches different deflecting mechanisms for the generation of a torque are used. In principal two ways are possible for the generation of a torque at the head portion of a torque wrench. The transducer is either rotatably fixed to the carrier and the grip holder is immoveable fixed to the carrier or, in the other way, the transducer is immoveable fixed to the carrier and the grip holder is moveably mounted on the carrier.
The operating devices having a grip holder which is moveable with respect to the carrier comprise a linear actuator with a spindle and a crank. By rotating the spindle by means of the crank the grip holder and thereby the grip of the torque wrench are deflected perpendicular to the carrier. Thereby a torque is exerted on the head portion which is fixed to the transducer. The torque wrench is tilted around an axis of the transducer. The grip is moved circularly in contrast to the linear movement of the grip holder and must, therefore, be held moveably in the grip holder.
The operating devices having a grip holder tightly mounted to an immovable carrier comprise a transducer rotatably fixed to the carrier with a deflecting lever or a gearing. The head portion of the torque wrench to be tested is tightly locked to the transducer by a transducer reception while the grip of the torque wrench is counter held by the grip holder. By application of a force on the deflection lever or by the rotary motion of the gearing a torque is exerted to the head portion via the transducer. In doing so the applied torque is measured by the transducer and compared with the torque displayed by the torque wrench or the torque predetermined at the torque wrench for a testing.
The grip holders of both kinds of operating devices comprise support surfaces which are made of steel or are coated with synthetic material. The torque wrenches to be tested usually have plastics grips and are provided with round or nearly round grips. During a measurement the grip in the grip holder is deflected horizontally. In doing so strong frictions of the grip surface on the support surface occur since a portion of the applied torque is used for overcoming the friction between the grip and the support. This leads to jerky motions during the deflection of torque wrenches and induces erroneous measurement results. In particular with very small torques to be tested severe distortion of measured values occurs being out of range of tolerance.
The known support devices for torque wrenches have the disadvantage of not being able to move the grip with little friction during a measurement. Instead they distort the measurement result because of abrupt motions of the torque wrench grips. This mainly occurs with torque wrenches having light grips since these are especially susceptible for lowest frictions at the support surface during the measurement. Torque wrenches comprising soft grips or grips with two components, for example with different plastics, also cause these undesirable and abrupt motions in the grip holder.